Candida albicans is the leading cause of fungal infections in the US and, Candida spp. now rank fourth among all pathogens in causing nosocomial infections. Virulence in this organism is probably multi-factorial and tissue-specific, since C. albicans is capable of infecting a number of diverse environmental sites (for example, the acid vaginal canal vs. the neutral pH of blood and tissues). Two-component, histidine kinases (HK) are environmental sensor, phosphorelay proteins of prokaryotes and lower eukaryotes whose activity results in transcriptional activation of genes associated with an adaptive response to stress. Among the HK genes of pathogenic fungi, recently, we isolated a C. albicans hybrid HK (CaHK1), which is unique structurally and functionally among all HK genes thus far described. A cahk1 null strain has been constructed and compared phenotypically in vitro and in vivo to parental and gene-reconstituted strains. In vitro, hyphae of null strains flocculate at pH 7.5, indicating that cell surface changes in hyphae are associated with a mutation in caHK1 The null is also avirulent in a systemic murine model but virulent in a rat vaginal mucosal model when compared to parental and gene- reconstituted strains. While Northern analyses indicate that CaHK1 is expressed in both acid and neutral pH media, we hypothesize that activity of Cahk1p may depend upon its state of phosphorylation. There are 3 specific aims in this proposal. 1. The influence of environmental factors (temp, pH, osmolarity) on the expression of CaHK1 will be measured in vitro using Northern analyses; post-translational modifications of Cahk1p will be determined. 2. We will evaluate the virulence of CaHK1 strain constructs in oral and vaginal models in order to extend our knowledge on the role of Cahk1p in virulence. 3. Cahk1p interactions with other proteins including down-stream effector proteins are to be identified. In summary, these studies will partially define the Cahk1p phosphorelay pathway and function of CaHK1 in the pathogenesis of candidiasis.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI043465-03
Application #
6488712
Study Section
Bacteriology and Mycology Subcommittee 2 (BM)
Program Officer
Duncan, Rory A
Project Start
2000-01-01
Project End
2003-12-31
Budget Start
2002-01-01
Budget End
2002-12-31
Support Year
3
Fiscal Year
2002
Total Cost
$327,278
Indirect Cost
Name
Georgetown University
Department
Microbiology/Immun/Virology
Type
Schools of Dentistry
DUNS #
049515844
City
Washington
State
DC
Country
United States
Zip Code
20057
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Chauhan, Neeraj; Calderone, Richard (2008) Two-component signal transduction proteins as potential drug targets in medically important fungi. Infect Immun 76:4795-803
Walia, Aditi; Calderone, Richard (2008) The SSK2 MAPKKK of Candida albicans is required for oxidant adaptation in vitro. FEMS Yeast Res 8:287-99
Chauhan, Neeraj; Kruppa, Michael; Calderone, Richard (2007) The Ssk1p response regulator and Chk1p histidine kinase mutants of Candida albicans are hypersensitive to fluconazole and voriconazole. Antimicrob Agents Chemother 51:3747-51
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Du, Chen; Calderone, Richard; Richert, John et al. (2005) Deletion of the SSK1 response regulator gene in Candida albicans contributes to enhanced killing by human polymorphonuclear neutrophils. Infect Immun 73:865-71
Kruppa, Michael; Krom, Bastiaan P; Chauhan, Neeraj et al. (2004) The two-component signal transduction protein Chk1p regulates quorum sensing in Candida albicans. Eukaryot Cell 3:1062-5
Singh, Praveen; Chauhan, Neeraj; Ghosh, Anup et al. (2004) SKN7 of Candida albicans: mutant construction and phenotype analysis. Infect Immun 72:2390-4

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